Some internal combustion engines such as gasoline engines and diesel engines are equipped with turbochargers. A turbocharger rotates a turbine using a pressure of exhaust gas from an engine, and drives a compressor with the aid of a rotational force of the turbine to supercharge the engine. An engine thus equipped with a turbocharger includes one equipped with a bypass line through which an outlet line of a compressor and an inlet line of a turbine communicate with each other (e.g., Patent Document 1).
The engine equipped with this bypass line is provided to efficiently operate an exhaust gas recirculation (EGR) system. An EGR system recirculates part of exhaust gas containing inert gases into intake air for a diesel engine so as to slow down combustion and reduce a combustion temperature in the diesel engine, thereby suppressing generation of nitrogen oxides (NOx) in exhaust gas. In this case, when a supply air pressure is higher than an exhaust pressure in the engine and hence exhaust gas is unlikely to flow to a supply air side, a bypass circuit is opened to cause part of intake air to flow into an exhaust pipe, thereby reducing the supply air pressure and facilitating exhaust gas recirculation. The control as described above is performed to make it possible to efficiently carry out EGR.
[Patent Document 1] JP 2001-165000 A (pages 9 to 10, FIG. 1)